Place a large skillet over medium-high heat with 2 turns of the pan of EVOO, about 2 tablespoons. Add the mushrooms and garlic to the pan, and cook, stirring occasionally, until deep golden brown, 6-8 minutes.
Add the sherry to the pan and cook until reduced, about 1 minute. Add the butter, parsley, some salt and pepper to the pan, and stir to melt the butter and combine. Serve warm alongside Crispy Potato and Ham-Wrapped Cod.